Device-to-Device (abbreviated as D2D) communications are a novel technology for allowing terminals to directly communicate with each other by multiplexing cell resources under the control of a cellular system. The D2D communications may increase the spectrum efficiency the cellular communication system, reduce the transmitting power of the terminal, and, to a certain extent, solve the problem of deficiency in spectrum resources of the wireless communication system. In the 3GPP document, D2D communications are referred as “Proximity Services”, and abbreviated as ProSe.